In general, a fuel cell is a power generation cell capable of generating electricity through combination of hydrogen and oxygen. Differently than general chemical cells, such a fuel cell has an advantage in that it is possible to continuously generate electricity, so long as hydrogen and oxygen are supplied, and production of environmental pollutants during power generation is reduced because the fuel cell employs a system of converting chemical energy into electrical energy through hydrogen-oxygen combination.
Among such fuel cells, a polymer electrolyte fuel cell currently exhibit or will exhibit, in future, high practical utility in that miniaturization is possible.
Such a polymer electrolyte fuel cell may secure desired power generation efficiency when a certain amount of moisture is supplied to the polymer electrolyte membrane of a membrane electrode assembly (MEA) in order to maintain an appropriate moisture content of the polymer electrolyte membrane.
As a method of humidifying the polymer electrolyte membrane, as mentioned above, there are a bubbler method, a direct spray method, and a membrane humidifying method. In particular, the membrane humidifying method is a method of bringing external fluid into contact with hollow fibers containing moisture, to increase the moisture content of the fluid, and then supplying the humidified fluid to an electrolyte membrane.
Such a hollow fiber membrane module basically has a structure in which an introduction case 10, a connecting case 30, and a discharge case 20 are connected to one another, as shown in FIG. 1.
In each of the introduction case 10 and discharge case 20, accommodation spaces 11 are vertically arranged while being spaced apart from each other by a predetermined distance. Hollow fiber bundles 40 are filled in the upper and lower accommodation spaces 11 of the introduction case 10, the connecting case 30, and the upper and lower accommodation spaces 11 of the discharge case 20.
External fluid is introduced into a fluid inlet 13 formed at one side of the introduction case 10, and is then introduced into the accommodation space 11 through a plurality of introduction windows 16 after moving along upper and lower channels 14 and an intermediate channel 12. Thus, the fluid comes into contact with surfaces of the hollow fiber bundles 40 and, as such, primarily absorbs moisture from the hollow fiber bundles 40.
Subsequently, the fluid secondarily absorbs moisture while passing through the connecting case 30, and then thirdly absorbs moisture while passing through the discharge case 20. Thereafter, the fluid is outwardly discharged through a fluid outlet after emerging from the accommodation spaces 11 of the discharge case 20 through discharge windows 21.
In the above-mentioned conventional structure, the upper and lower channels 14 and intermediate channel 12 in the introduction case 10 have the same cross-sectional area.
Due to such a structure, when external fluid is supplied to the interior of the introduction case 10 through the fluid inlet 13, the external fluid strikes round corners of the upper and lower accommodation spaces 11 while entering the fluid inlet 13. As a result, as shown in FIG. 2, momentary stagnation zones may be formed around an inlet of the intermediate channel 12 and, as such, the pressure of the fluid in such zones greatly increases (as indicated by dots).
Since the intermediate channel 12 has a reduced size, as compared to a region around the inlet thereof, the flow velocity of the fluid in the intermediate channel 12 is abruptly increased, and is then gradually reduced as the fluid flows toward an end of the intermediate channel 12 opposite to the inlet (Areas exhibiting an increase in flow velocity are indicated by dots.).
Meanwhile, the pressure distribution in the intermediate channel 12 is established such that the fluid flowing through the intermediate channel 12 exhibits very low pressure in a section from the inlet of the intermediate channel 12 to a point spaced apart from the inlet by a certain distance while exhibiting increased pressure as it flows toward the end opposite to the inlet.
That is, in the conventional structure, there may be a phenomenon in which the internal pressure of the intermediate channel 12 in the introduction case 10 is lower than in the upper and lower channels 14 of the upper and lower accommodation spaces 11 and, as such, the flow velocity of the fluid in the intermediate channel 12 is higher than those of the upper and lower channels 14.
Due to such a phenomenon, that is, a difference between the internal pressure of the intermediate channel 12 and the internal pressure of each of the upper and lower channels 14, the fluid passing through the intermediate channel 12 may not be smoothly introduced into each accommodation space 11 and, as such, may be introduced into the intermediate channel 12.
As a result, there is a great difference between the flow rate of the fluid supplied through the intermediate channel 12 and the flow rate of the fluid supplied through the channel 14 around each accommodation space 11.
Furthermore, even in the upper and lower channels 14 and intermediate channel 12 around the accommodation spaces 11, an increase in pressure and a reduction in flow velocity is exhibited at points distant from the fluid inlet 13.
Since the intermediate channel 12 and upper and lower channels 14 each exhibit pressure deviation of different sections thereof, the flow rate of the fluid introduced into each accommodation space 11 in each channel is gradually increased toward the channel end opposite to the fluid inlet 13 such that the flow rate is higher at the introduction window 16-1 toward the channel end than at the introduction window 16 toward the fluid inlet 13.
That is, the hollow fiber bundles 40 in the introduction case 10 cannot uniformly contact the fluid throughout the entire section thereof due to the difference between the internal pressure of the intermediate channel 12 and the internal pressure of each of the upper and lower channels 14 in the introduction case 10 and pressure deviation of different sections of each channel.
As can be experimentally demonstrated, referring to FIG. 4, the flow rate of the fluid passing through each of the windows 4, 5, 6, 7, 8, and 9 is considerably lower than the flow rate of the fluid passing through each of the windows 1, 2, 3, 10, 11, and 12, as in the following Table 1.
In addition, it may be seen that, even in the intermediate channel 12 and upper and lower channels 14, the flow rate of the fluid passing through the windows is gradually increased toward the channel end opposite to the fluid inlet such that the flow rate is considerably higher at the introduction windows 3, 6, 9, and 12 toward the channel end than at the introduction windows 1, 4, 7, and 10 toward the fluid inlet.
TABLE 1Flow Rate (%) of Fluid through Each Window{circle around (1)}{circle around (2)}{circle around (3)}10.910.912.6{circle around (4)}{circle around (5)}{circle around (6)} 4.1 4.6 6.7{circle around (7)}{circle around (8)}{circle around (9)} 3.8 4.5 7.2{circle around (10)}{circle around (11)}{circle around (12)}11.111.212.5